Subsurface safety valves are well known in the art. They are used in a well, such as an oil or gas well, to provide a safety shut off in the event of a well failure. A subsurface safety valve is typically installed in a production tubing string and run downhole into the well. The valve is typically a normally-closed valve, in that the valve automatically shuts under default conditions, such as when the hydraulic control fluid to the valve is interrupted. When shut, the safety valve does not allow contents from below the safety valve, such as production fluids, to continue flowing to the surface of the well. Uncontrolled flowing production fluid, such as gas or other hydrocarbons, may cause explosions or otherwise damage surface facilities and/or cause environmental damage in the event of a well failure.
Referring to FIG. 1, typically, a valve element, such as a disk-shaped flapper 10, is used to seal off the production fluid in a main bore 50 of the safety valve. The flapper 10 is attached to a hinged valve element known as a flapper mount, and can be pivoted to an open position to allow production fluid to flow. The flapper 10 is typically forced open by a flow tube 5 mounted in a bore 50 of the subsurface safety valve. The flow tube 5 slidably engages the flapper 10 overcoming the torsion spring force maintaining the flapper closed. The flow tube 5 moves longitudinally down the bore 50 and pushes the flapper 10 out of the main bore flow path. In many designs, an actuator 15 having a piston in a side chamber adjacent to the main bore 50 is remotely actuated to cause the flow tube 5 to move down to engage the flapper 10 and force the flapper 10 out of the flow path. A power spring 25 inside the spring housing 30 is compressed between the flow tube 5 and a shoulder within the spring housing 30 to force the flow tube 5 up to allow the flapper 10 to enter and close off the main bore 50.
A subsurface safety valve with a spring housing containing a flapper mount, hard seat and a sealing component is typically manufactured in several pieces. The spring housing usually forms one piece, and it contains the flow tube with an upwardly biasing spring, and an adjacent piston. The flapper mount, which includes the flapper and hinge, and a sealing component, generally form one or more other pieces. The flapper mount attaches to the lower end of the spring housing through a variety of connection methods, usually a threaded connection, which screw together. The sealing component is usually trapped between the hard seat and the flapper mount. When the flapper is closed, the outer perimeter of the flapper presses against an annular opening of the main bore of the safety valve to seal the well. The contact area between the flapper and the main bore of the safety valve usually comprises both a “hard seat,” which is a metal-to-metal contact between the flapper and the bore, and a “soft seat,” which is a metal-to-non-metal contact between the flapper and the sealing component.
Safety valves thus comprised have several leakage paths. One path is through the hard seat/soft seat interface when the flapper is closed. Another leakage path is through the connection between the flapper mount and the spring housing. A third leakage path is through the connection between the hard seat and spring housing or flapper mount.
When the components of the safety valve assembly (the flapper mount, hard seat and spring housing) are individual components, the tolerance of the connections between the components interacts with the design tolerances of the flapper, making the overall flapper design less reliable and its manufacture more difficult. One way to eliminate the leakage paths through these connections and the interaction (or stack up) of the tolerances between the flapper mount, hard seat and the spring housing is to integrate the flapper mount, hard seat and spring housing designs creating one piece. Removing the connection between the flapper mount, hard seat and the spring housing increases the reliability of the seal by removing multiple leak paths and eliminates the interaction of tolerances between the individual components and the flapper design.